Apparatus and method for making flexible tubing with helically wound heating conductor

Abstract

A helically wound and helically ribbed plastic tubing incorporating an electrically conductive heating wire and an apparatus and method for making the tubing are disclosed. A plastic ribbon is wound about an axis into a tube with one edge of each lap overlapping and heat-bonded to an edge of the preceding lap as the tubing is rotated; a conductive wire is embedded in the ribbon; and a bead is applied and heat-sealed onto the tubing, encapsulating the conductive wire during rotation of the tubing, providing a unitary structure including a conductive wire integral to a flexible tubing having a corrugated crevice-free outside and a smooth inside. Coolant is applied to the tubing for cooling the unitary ribbon, wire and bead tubing and to assist in advancing the tubing along the axis.

What is claimed is: 
     
       1. A thin-walled, flexible and collapse-resistant plastic tubing having a substantially smooth bore for conducting tidal air flow and a helical outer support bead, the tubing including an electrical resistance conductor for heating tidal air flow in said bore, said tubing comprising: a flexible tubing wall formed of elongate thermoplastic ribbon having opposite side edges, said ribbon being helically wrapped on itself to overlap said opposite side edges a certain amount forming a helical lap joint whereat opposite side edge portions of said ribbon are heat-bonded to one another so that a thin-walled elongate tubular body is formed;   an elongate electrical resistance heating conductor disposed helically around and along said flexible tubing wall adjacent to an outer one of said opposite side edges; and   an elongate thermoplastic support bead disposed helically around and along said flexible tubing wall atop both said helical lap joint and said electrical resistance heating conductor and being heat-bonded to said tubing wall to form a unitary body therewith encapsulating said electrical resistance heating conductor, said elongate thermoplastic support bead having a thickness between said electrical resistance heating conductor and ambient which is substantially greater than said ribbon, and having a heat transfer conductivity which is substantially less than said ribbon;   whereby said electrical resistance heating conductor is insulated from said tidal air flow by only a single thickness of said ribbon, but is insulated from ambient conditions outwardly of said tubing by said support bead.   
     
     
       2. The tubing of claim 1 wherein said elongate plastic ribbon comprises a polyester elastomer. 
     
     
       3. The tubing of claim 1 wherein said elongate support bead comprises a thermoplastic rubber. 
     
     
       4. The tubing of claim 1 wherein said elongate plastic ribbon and said elongate support bead comprise identically the same material. 
     
     
       5. The tubing of claim 1 wherein said resistance heating conductor is a nickel chromium alloy. 
     
     
       6. The tubing of claim 1 wherein said resistance conductor for heating includes a pair of parallel conductors spaced apart and insulated from one another. 
     
     
       7. The tubing of claim 6 wherein said resistance conductor for heating includes a jacket carrying said pair of conductors in spaced apart parallel relationship to one another. 
     
     
       8. The tubing of claim 7 wherein said pair of conductors is electrically connected together adjacent a distal end of a length of said tubing. 
     
     
       9. A thin-walled, flexible and collapse-resistant plastic tubing having a wall with a substantially smooth bore for communicating fluid, and a helical radially outwardly extending support bead carried upon said wall, the tubing including an electrical resistance conductor embedded within said support bead, which resistance conductor has a comparatively conductive heat transfer relationship to fluid within said bore and a less conductive and more insulative heat transfer relationship with ambient conditions outside of said tubing wall, said tubing comprising: a flexible tubing wall formed of elongate thermoplastic ribbon having opposite side edges, said ribbon being helically wrapped on itself to overlap said opposite side edges a certain amount forming a helical lap joint whereat opposite side edge portions of said ribbon are heat-bonded to one another forming a thin-walled elongate tubular body;   an elongate electrical resistance heating conductor disposed helically around and along the length of said flexible tubing wall atop said elongate thermoplastic ribbon and adjacent to an outer one of said opposite side edges; and   an elongate thermoplastic support bead having a thickness in the radial direction of said tubing which is substantially greater than said ribbon and being disposed helically around and along said flexible tubing wall atop both said helical lap joint and said electrical resistance heating conductor and being heatbonded to said tubing wall to form a unitary body therewith and encapsulating said electrical resistance heating conductor;   whereby said electrical resistance heating conductor is insulated from said fluid by only the single thickness of said elongate thermoplastic ribbon forming said tubing wall but is insulated from ambient conditions by said support bead, and said support bead provides collapse-resistance to said tubing wall.   
     
     
       10. The tubing of claim 20 wherein said elongate plastic ribbon is formed of a polyester elastomer. 
     
     
       11. The tubing of claim 9 wherein said elongated support bead is formed of a thermoplastic rubber. 
     
     
       12. The tubing of claim 9 wherein said elongated plastic ribbon and said elongate support bead are formed of identically the same material. 
     
     
       13. The tubing of claim 9 wherein said resistance heating conductor is nickel chromium alloy. 
     
     
       14. The tubing of claim 9 wherein said resistance conductor for heating includes a pair of parallel conductors spaced apart and insulated from one another. 
     
     
       15. The tubing claim 14 wherein said resistance conductor for heating includes a jacket carrying said pair of conductors in spaced apart parallel relationship to one another forming a twin-lead heating cable, said twin-lead heating cable being disposed with one of said pair of conductors adjacent to said outer one of said overlapped side edges of said elongate thermoplastic ribbon and with the other of said pair of conductors adjacent to said one conductor in side-by-side relationship and with each conductor of said pair separated from said thermoplastic ribbon only by said jacket. 
     
     
       16. The tubing of claim 15 wherein said pair of conductors is electrically connected together adjacent a distal end of a length of said tubing.